The present invention relates to an inkjet drawing method and an inkjet drawing device for recording an image on a sheet-like image recording medium by an inkjet recording method, and in particular, to an inkjet drawing method and an inkjet drawing device for forming an image on, for example, a lithographic printing base plate for use in, for example, a plate making apparatus for producing a printing plate for lithography by an inkjet recording method.
In lithography, a surface of a printing plate is provided with a printing ink receiving (i.e., ink receptive) region and a printing ink repulsive (i.e., ink repellent) region in correspondence with an original image, and printing is performed by causing printing ink to adhere to the ink receiving region. In ordinary cases, a hydrophilic (i.e., ink repellent) region and a lipophilic (i.e., ink receiving or ink receptive) region are formed imagewise on the surface of a printing plate, and the hydrophilic region is made ink repulsive (i.e., ink repellent) by using dampening water.
A printing plate on which an image is formed has been conventionally produced (i.e., prepared) for each color according to the following procedure. When an original is a monochromatic original, a silver salt photographic film (e.g., lith film) is exposed and developed in an analog or digital manner to output a film plate bearing an image included in the original as it is. When the original is a color original, the original is subjected to color separation into, for example, the respective colors of C (cyan), M (magenta), Y (yellow), and K (black), and a silver salt photographic film is exposed and developed for each color in an analog or digital manner to output a film plate bearing an image of each color included in the original. The film plate is used to expose a diazo resin or a photopolymer photosensitive material (presensitized plate). Then, for example, a non-image area is dissolved and removed by using mainly an alkali solution, whereby the printing plate is produced.
With the improvement in digital drawing technology and a demand for an improvement in efficiency of a plate making process, a large number of systems each capable of directly drawing digital image information on a presensitized plate (i.e., plate in which a photosensitive layer, a heat-sensitive layer, or the like is formed on a printing base plate) have been proposed in recent years. A known example of such system capable of directly drawing digital image information on a presensitized plate is a system that records an image on, for example, the photosensitive layer or heat-sensitive layer of a printing base plate by using laser in an optical mode or a thermal mode, However, in this plate making method, plate making is generally performed by dissolving and removing a non-image area through the treatment (of, for example, the photosensitive layer or heat-sensitive layer) of the exposed printing base plate with an alkali developer after laser recording in each of the optical mode and the thermal mode. The discharge of an alkali waste liquid as it is is not preferable in terms of environmental protection, so the disposal of the alkali waste liquid is needed. In addition, a method involving the use of laser requires an expensive and large device.
In order to solve the problem, there has been attempted to use an inkjet recording method which is an inexpensive and compact drawing mode. The direct formation of an image on a printing base plate by an inkjet recording method results in the production of a printing plate without, for example, dissolving or removing a non-image area. In addition, a device using the above method can be small.
JP 2004-322560 A and JP 2004-358769 A each disclose, as a recording device that employs an inkjet recording method, an inkjet printer using ultraviolet (UV) curable ink (hereinafter referred to as “UV ink”) which is of such a type that the UV ink is ejected as an ink droplet from an inkjet head. The inkjet printer using the UV ink has, on a side of an inkjet head, UV irradiation means for radiating ultraviolet light to a UV ink droplet ejected from the inkjet head and caused to impinge on the surface of a print medium to cure the UV ink droplet. Immediately after the UV ink has been caused to impinge as a droplet on the surface of the print medium as described above, ultraviolet light is radiated from the UV irradiation means to the impinged UV ink droplet to dry and cure the UV ink quickly, whereby an image is formed on the print medium.
The inkjet printer disclosed in JP 2004-322560 A includes therein a UV lamp that generates high heat as the UV irradiation means. Accordingly, in order that a printer portion to be irradiated with UV light radiated from the UV lamp which is the UV irradiation means may be prevented from being heated to a high temperature at a position where each of the inkjet head and the UV irradiation means is on standby, cooling means for cooling a cover on which UV light radiated through a window in the bottom surface of the UV irradiation means impinges is provided.
On the other hand, in the device disclosed in JP 2004-358769 A, a UVLED or UVLED array is used as the UV irradiation means, whereby the drawbacks of a UV lamp such as a high-pressure mercury lamp or a metal halide lamp which is large and consumes large electric power, i.e., generates high heat are eliminated, the energy consumption of the UV irradiation means is reduced, and a reduction in size of the UV irradiation means is achieved. In addition, JP 2004-358769 A discloses an example of a constitution in which an inkjet head and the UV irradiation means are integrated to be moved, and an example of a constitution in which they are moved as separate bodies.